It is sometimes difficult to evaluate video on a device, or even a machine structured to evaluate video when a simulated output cannot be accurately viewed on an attached display. For instance, a video engineer may wish to see how a particular video would look to a viewer watching a consumer LCD (Liquid Crystal Display) television, a producer viewing a studio CRT (Cathode Ray Tube), an engineer in a broadcast center, or an engineer in a product development laboratory. Currently some quality analyzers, such as the picture quality analyzer PQA500 from Tektronix of Beaverton, Oreg. incorporates display models, simulating light and the human vision system in order to quantify differences for these types of applications. However, there is no way for users of such quality analyzers to directly experience the perceptual stimuli that are simulated. Instead, the video is rendered on the display that is used in conjunction with the quality analyzer. Further, display manufacturers have an unmet need to be able to automatically evaluate virtual designs, before a product is built. However, without being able to directly see the differences among display design options, much useful information is hidden from the display engineers.
Although mathematical solutions exist for converting video from one color space to another, such as YCbCr to RGB to CIE 1931 XYZ linear light representation, such solutions do not take into account various display variation from standard RGB. For instance, XYZ coordinates of the purest red, green, or blue represented by the digital video may not match the corresponding XYZ coordinates on the end display. Further, these relationships do not account for a mis-match in gamma values, i.e., a parameter used to represent the non-linear transfer function between the input signal and output light intensity, because the equivalent gamma of a display may not match the gamma in any corresponding standard.
Even in cases where the primaries and gamma do match a standard, such as SMPTE-C for standard definition, or ITU 709 for high definition video, white point calibration is often intentionally set to a non-default value. For instance, a computer monitor typically set at 9500° default color temperature may instead have its white point set to 6500° to match a television default color temperature. This white point calibration allows a display with one set of primaries to come close to looking like a display with another set of primaries. However, such conversion is not included in the color conversion formulae mentioned above, and does so by shifting colors in a way that many colors in the gamut are lost.
Other potential solutions require expensive and specialized equipment to physically measure output from a first display to create a conversion process from a first to a second display, which is expensive, complex, and too computationally intensive to provide a generalized solution. In addition, it requires an actual display to be measured, and not a modeled display. Further, no system, including the direct measuring systems, includes a way to compensate for response times of LCDs between the end of a video frame and the beginning of a next one. This leads to unacceptable and sometimes very perceptible display artifacts, such as motion blur.
Embodiments of the invention address this and other limitations of the prior art.